Low-frequency-signal repeater.



n.w. NICHOLS. LOW FBEQUENCY SIGNAL REPEATER. APPLICATION "LIED SEPT. 2.I915- Phtented Feb. 26, 1918.

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UNITED STATES PATENT orrron.

HAROLD W, NICHOLS, 0F MAPLEWOOD, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEWYORK.

LOW-FREQUENCY -SIGNAL REPEATER.

Specification of-Letters Patent. v

Patented Feb. 26, 1918.

Application filed September 24, 1915. Serial N 0. 52,509.

.vented certain new and useful Improve ments in Low-Frequency-SignalRepeaters, of which the following 13 a full, clear, concise.,and exactdescription. Y

This invention relates to a method of and apparatus for the repeating ofmessages from, one submarine cable or similar line to another. Itsobject is to amplify and re peat in one line low frequency currentsoriginating in another without destroying the property of duplexoperation of either line, and' to perform this operation efiiciently andwith fidelity.

These objects are'aocomplished by employing auxiliary circuits betweenthe two lines in question, supplying these circuits with lternatingcurrent, varying the characteristics of the currents in these circuitsby means of the incoming signal, and translating these variations to theforms of signals to be transmitted to the outgoing lines. Theseoperations are desirable for reasons which will appear in the followingdiscussion of the problems involved in the efiicient repetition ofsignals betweentwo duplex cables, telegraph lines or, other circuitscarrying low frequency signaling currents.

It has been found that repeaters of the mechanical type, for example,those in which an electromagnetic receiving device actuates amicrophone, are not suitable tor 'use in connection with .lowfrequencysignaling circuits. On the' other hand, the thermionic repeater of theaudion type, by reason of its high sensitiveness and its freed'o'm fromdistorting effects, is especially fittedfor this kind of work.Thisrepeater consists of an electron-emitting cathode, an anode, and anauxiliary electrode, all inclosed in an evacuated vessel.

'An important feature of this device in connection with this problem isthat its input circuit and its output circuit necessarily have one pointin-common, since the repeater has but three terminals. This factintroduces into the problem of repeat?- from one duplex cable to anothersome di culties which are overcome in this invention;

and which will be explained in connection with the drawings.

In these drawings, Figure 1 shows the circuit arrangements of two duplexcables terminating at a repeater station; Fig. 2 shows a method ofrepeating from one of these cables to the other in accordance with thisinvention; and Fig. 3 shows a modified form ofthe' invention in whichgreater amplification of signals is secured. In all. of these figures,corresponding parts are denoted by like numerals.

Referring to Fig. 1, 1 and 8 are cable condoctors and 2 and 4 theirbalancing artificial cables introduced, as usual, to permit duplexoperation in connection with the condensers 5. 6 represents a groundconnection.

In receiving a signal over cable 1 the re I ceiving instrument isconnected to the re; ceiving ternnnals 7-8, and in sending through thiscable an ele'otromotive force is the condensers 5 are equal, thissending electromotive force produces no difi'erence of potential betweenthe terminals 7-8, and, consequently, the receiving instrumentv is notaffected in sending fromthe station at which it is located. Duplexoperation is therefore possible over these two cables, and its successdependsupon the accurate simulation'of the actual line by its artificialline.

'Now, if it is-desired to relay signals from cable 1 to cable 3, it willbe necessary to connect the receiving terminals 7 -8 of cable 1, throughan amplifier, with the transmitting terminals 1237, of cable 3, and similarly terminals 1011 with terminals 359 and, as stated before, it isdesirable to use the thermionic amplifier for this purpose.

connection between input and output circuits, and an examination of Fig.1 will Qaow that no matter how such an amplifier is connected fromthereceiving terminals of one cable to the transmitting terminals of theother, it will short-circuit one of the lines and destroy the propertyof duplex operation- 1 There must be 11;; conducting path, except forthe earth, :{xfom one cable to the other if duplex operation is to bemaintained. To

, amplifier, to the transmitting terminals of the other cable.

This is the invention of another and is, moreover, open to theseriousobjection that the transformation of currents, ofthe wave forms andfrequencies used in tclegraphy,

is not eflicient and that it requires specially designed and expensivetransformers. This invention eliminates the necessity for inefiicientlytransforming currents of the low fundamental frequency and complicatedwave form here encountered, and substitutes therefor efiicienttransformation of sinusoidal currents of a single relatively highfrequency in a manner more completely de scribed in connection with Fig.2 which represents a preferred form of'the invention, and also inconnection with Fig. 3 in which an additional amplifier is used tosecuregreater amplification.

Referring to 'Fig. 2, numerals 35, 37 and 1 to 12 inclusive, representtwo duplex cable terminals, as explained in connection with Fig. 1. 13is a thermionic amplifier of the audion type whose function is toamplify the potential difi'ere'nceover the resistance li'inscrtedbetween the receiving terminals, 78 of the first cable, Its action is asfol- .lows: When a potential difference is established over the inputterminals of 13, the effect is to change the current set up by thebattery-16 in the output circuit of'the amplifier, which includesresistance 15. The

change in voltage drop over 15, due to that input otential difference,is much greater than t e latter. Another function of the amplifier 13 isto prevent the reaction upon the incoming cableof the current in theapparatus next to be described. This effect is secured because thethermionic amplifier is a nnilaterahdevice and permits the transfer ofpower in but one direction through it.

17 is another amplifier adapted to act as an oscillation gcneraton Anyamplifier, when arranged so that power may be fed back from its outputcircuit to its input circuit, for example, by inductively connectingthese circuits, will oscillate freely if the amplifying power issufiiciently large. The

power, represented by this free oscillation isdrawn from thebatteryinthe output circuit. In the oscillator of the figure a tuned circuit,comprising coil 19 and condenser 20, is included in the output circuit,while the input circuit in ludes half the coil 19, due to the fact thatt e filament or cathode of the repeater is connected to cpil9 at thepoint 21. Since the two halves the coil further increase 19 are relatedby mutual inductance, the two circuits are inductively connected and thedevice acts an alternating current generator of oscillations whosefrequency is de termined by the tuned circuit 1.9 20.

The input circuit of this oscillating amplifier is also connected acrossresistance 15, by which connection the amplified signal voltage isimpressed upon the input circuit of 17, preferably through the battery18, which is used to maintain the potential of the grid at a suitablevalue with respect to that of the filament. The effect of impressingthis variable signal v'oltage upon the amplifier 17 is to change itsamplifying power and, therefore, to vary the amplitude of thealternating current in its output circuit in accordance with the signalreceived oven the cable 1. This method of modulating. the amplitude ofan alternating current is not the invention of this applicant and is notclaimed in this 'ipplicaton.

The coil 19 is inductively coupled to coil 22 of the tuned circuit22--24, and since. now .a pure alternating current of relatively highfrequency is in question, the transformation by the transformer 19-22 isefiicient in contrast to the ease in which the signal waves themselvesmust be transformed.

It is now necessary to rectify this modulated current so that the effectof the-high frequenc ylplternating current shall be elimia lowimpedance) as follows: Suppose that an impulse of positive potentialwith respect to the filament 'is impressed upon the grid circuit so thatthe grid becomes positively chargcd. This char e will now be ra idlyneutralized by the ow of electrons rom the heated filament to the grid.If now this positive impulse is followed by a negative impulse, thenegative charge remaining upon the grid will be still current in theaudion, whose magnitude is governed by the charge upon the grid, will bedecreased more than would be the case if the negative charge firstmentioned had been "free to leak away. It is prevented from so doing bythe condenser 26. Howand, therefore, the space ever, it is not desirableto retainthis negative charge upon the grid indefinitely, and to preventthis the resistance 25 is shunted about the condenser. This resistanceis so large that the leak of current through it in a time comparablewith the period of the highfrequency oscillation is small,butthisleakage path is marleof sufficiently low resist ance to permitthe complete discharge of the 7 grid in the longertime elapsing betweensigelement. As in the operation of any recti-- sense 1 nals. The efi'ectof this combination of resistance and. capacity is, therefore, toincrease therectifying effect of the thermlonic fier, it'responds onl tothe envelop of the high frequency oscillations, that is, it produces inits output circuit a direct current upon which is superposed a currentof the wave form of the'signal received from .the

first cable. The high inductance choke coil -27 permits the free assageof the necessary direct current in t e output circiiit of 23 whileofiering a high impedance to the signal currents superposed upon it,which latter are therefore impressed upon the transmitting terminalsl2'*-37 of the outgoing cable, preferably'through condenser28. Acondenser 32 is preferably added in the output circuit of am lifier' 17to prevent the short-circuiting o resistance 15. A similar system of...circuits leads in the opposite direction-{that is, from the receivingterminals lO-l'l'to the transmitting terminals 359.of the first cable.

Fig. 3 represents an arrangement similar to Fig.2 eiicept that anadditional amplifier is added to still further increase the energy "ofthe repeated signals impressed upon the second line. In this arrangementthe tuned circuit 22, 24 instead of being directly connected to therectifyin element23, is now connected to the input e ectrodes of thethermionic am lifier 30. The output circuit of this a'mpli er iscompleted through the re sistancc 31 and contains an energizing bate.

' tery as shown. The rectifying element 23 is then connected across theterminals of resistance 31.. This modifies. the operation of the deviceonly in so far as it increases the ,voltage supplied to the rectifier,and consequentlyvincreases the value of the rectified current. Anadvantage secured by tlieuse of this amplifier, in addition to thegreater 'power obtained, is that the thermionic element, when acting asa rectifier, is more efli cient when the voltage impressed across itsinput terminals is large. In all other respects this arrangement issimilar to that s own in Fig-2.

Although this invention has been shown as applied to the amplificationof signals from one duplex cable to another, it is obvious that itsadvantageous use will not'be restricted to thi's'type of apparatus. Itsuse may be desirable in any system requiring thetransformingor'repeating of low frequency si als. I ifhat is claimed.is:

L In combination with two duplex lines having receiving and transmittingterminals adapted for electrical. signaling with .low frequencycurrents, a device for relay- "ing signals from one to the other of saidlines, a .similar'device for relaying signals in the opposite direction,means for pro-.

viding for non-interference between said devices, each of said devicesconsisting of a circuit, means for producing therein electricaloscillations capable of eificient trans formation, means for varying thecharacter of said oscillations in accordance with a signal received fromone of said lines, said varying means comprising a resistance shuntedacross the receiving terminals of said line, anamplifier having anoutput cirwit, and a transformer whereby the effect of said variableoscillations is communicated to said amplifier and therebyaug- "mented,a detector connected with said output circuit, and means for impressingupon the other of said lines the detected current. 2. In telegraphy, twoduplex lines adapted to transmit low frequency signals, each linehaving'separate receiving and transmitting terminals, the combinationwith the transmitting terminals of'one line and the receiving terminalsof the second line, of a circuit containing a modulator wherein isdeveloped an alternating CUI1Ilt,. Jf a ther 'mionic amplifierinterlinked with said circult and with the receiving terminals of thefirst of said lines whereby the amplitude of the alternating current isvaried in accordance with the electrical signals in said line.

of a transformer for inductively communicating the oscillations in saidcurrent to a second circuit, of a thermionic detector whose inputelectrodes are connected to said second circuit, the transmittingterminals of said line being so connected to the output circuit of saiddetector as to be in fluenced by the rectified currents appearing insaid output circuit.

3. In telegraphy, two duplex lines adaptedto transmitlow-frequencysignals, the

combination with the receiving terminals i transmitting terminals. v

4, In telegraphy, two lines adapted to transmit low frequency signals,each line having separate receiving and transmitting term'inals, thecombination with the'trans-" mitting terminals of one line, and thereceiving terminals of the second line, of'a resistance shunted acrosssaid receiving terminals, of an oscillati )1! generator wherein isdeyeloped an alternating current, of a therng' omoiamphfierhaving aninput cir- .cuit and an output circuit, said resistance serving, as ameans, for impressing the electrical signals insaid line uponsai'd inputcircuit, of means for directly impressing the amplified signals in saidoutput circuit upon said oscillatlon enerator, whereby the amplitude ofthe afiernating current is varied in accordance with said signals, of ather mionic detector having an input, circuit and an output circuit, ofa transformer for inductively communicating the oscillations insaid-current to the input circuit of said detector, the transmittingterminals of said line being so connected to theoutput circuit of saiddetector as to be influenced by the detected current appearing in saidoutput circuit.

5. In telegraphy, a duplex line, a vacuum tube repeater containing acathode and an auxiliary electrode said line terminating in saidelectrodes and 6. In telegraphy, a duplex line, two shunt paths acrosssaid line, one of said paths auxiliary apparatus as sociated with saidline and tube for the twoway transmission of signals. I

across said resistance upon t e input elec trodes of said repeater, andmeans comprising a second repeater connected to an inter- I mediatepoint of said capacity path for impre sing si alin without e ective yimpressing them ,upon

said first repeats 7. In telegraph a duplex line, two shunt paths acrosssaid line, one of said paths comprising a resistance, the other be ng acapacity path, a vacuum tube repeater having its input electrodesshunted across said resistance, andmeans comprising a second currentsupon said line vacuum tube repeater connected to the midpoint of saidcapacity path for impressing signaling currents upon said line withoutimpressing them upon said first repeater.

1n witness whereof, I hereunto subscribe my name this 23rd day ofSeptember, A. D.,

HAROLD W. NICHOLS.

